paleo-Pearl River Research Articles

Detrital zircon signals of the late Eocene provenance change of the Pearl River Mouth Basin, northern South China Sea

A provenance change driven by tectonic and climatic forcing records the surface geodynamic processes, and is of great significance for our understanding of evolving continental margins. The Paleogene succession in the Pearl River Mouth Basin (PRMB), northern South China Sea (SCS), records the variation of sediment-routing systems and thus can reveal provenance changes and their association with the regional paleogeographic evolution on the South China margin. We use U–Pb ages and the Eu/Eu* anomalies of detrital zircons from Paleogene samples in Huizhou Sag, northern PRMB to reconstruct the sediment-routing system and the crustal thickness of the South China margin, respectively. The results show that from the middle Eocene to the upper Eocene there was a rapid increase in proportion of old-age zircon populations (>200 Ma), reflecting a provenance change from the intrabasinal Mesozoic basement to the extrabasinal South China Block. Moreover, the Eu/Eu* anomalies in detrital zircons suggest that during Cretaceous the crustal thickness increased from ca. 40 km to ca. 70 km in the South China margin, corresponding to the uplift of the extensive Coastal Mountains along the South China margin. The substantial rock uplift is believed to be related to the subduction between the Cretaceous Izanagi Plate and the South China Block. A new paleogeographic pattern is reconstructed, where we relate the late Eocene provenance change to the relief generated by the Cretaceous orogenic event. Firstly, due to the rain shadow effect, the uplift of the Coastal Mountains prevented pacific air from reaching into the South China hinterland, causing the northwestern side of the Coastal Mountains to be arid whereas the southeastern side being humid. Then, on the humid southeastern foothills, the paleo-Pearl River originated from the Late Cretaceous to the middle Eocene and transported more and more sediments from the South China Block to PRMB since the late Eocene, causing the provenance change from the intrabasinal basement to extrabasinal South China Block.

Geochemistry and provenance of Oligocene to middle Miocene sandstones in the Qiongdongnan Basin, northern South China Sea

The Qiongdongnan Basin (QDNB) is a petroleum-bearing basin in the northern margin of the South China Sea (SCS). Provenance analysis is an important tool in petroleum exploration and is helpful in predicting the distribution of good reservoirs in areas with less drilling. However, the provenance of the QDNB remains controversial, and further research is needed. Here, we apply whole-rock geochemistry, petrography, and heavy minerals combined with published detrital zircon U-Pb ages to constrain the provenance of Oligocene to middle Miocene sandstones in the QDNB and the tectonic environment of their deposition. The Oligocene to middle Miocene sandstones from the QDNB are geochemically immature. These sandstones were derived from a weakly weathered source area characterized by dominantly felsic igneous rocks, with a particular slight addition from recycled sedimentary sources. And the Lingshui Formation underwent less weathering than the upper and lower strata. The tectonic setting of the sandstones in the basin belongs to a continental island arc (CIA) or an active continental margin (ACM). Heavy mineral assemblages and detrital zircon U-Pb ages reveal sediment input from multiple sources. Hainan Island was a major and continuous source area contributing to the basin from the early Oligocene to the middle Miocene. In addition, intrabasinal uplift regions could have supplied material to local areas. While these sedimentary source patterns appear to have changed very little in the late Oligocene, a provenance from central Vietnam was explicitly discerned in the western QDNB in the late Oligocene. It is possible that the paleo-Pearl River supplied large volumes of sediment to the eastern QDNB from the late Oligocene to the early Miocene.

Insights into evolution of a rift basin: Provenance of the middle Eocene-lower Oligocene strata of the Beibuwan Basin, South China Sea from detrital zircon

Investigating rift basins and their provenance is difficult because their tectonic framework is continuously evolving. The Beibuwan Basin in the South China Sea is a typical rift basin that shares many characteristics of major rift basins worldwide. We present new detrital zircon UPb ages from the Beibuwan basin and, by combining with published data from surrounding drainages, are able to define its potential sources and to investigate its provenance evolution from the middle Eocene-lower Oligocene. Detrital zircon age spectra from distinct structural units and formations of the rift basin reveal spatial-temporal differences in provenance. In the middle-upper Eocene, a similar age pattern with major peaks at 263–253 Ma and 450–416 Ma is preserved across the basin and suggests that sediment was uniformly derived from the Yunkai Massif and Hainan Island. In contrast, during the lower Oligocene the basin displays markedly diverse ages with peaks at 250–243, 416, 756, 967–945, 1096–1084 Ma. The increase of Neoproterozoic zircons in the lower Oligocene stratum suggests that a major change in provenance occurred, most likely associated with the reorganization of the paleo-Pearl River along its central reaches due to a topography reversal associated with the uplift of Tibet and the onset of seafloor spreading in the South China Sea. Our spatial analysis of ages indicates that during the lower Oligocene, the detrital input varied across the basin. Rifting processes in the Beibuwan Basin generated multiple isolated depocenters separated by intra-basinal highs. The basin's architecture greatly affected sediment routing, with structural highs serving as barriers to sediment transport. Sediment provenance in the Beibuwan Basin is primarily controlled by drainage evolution and isolated depocenters associated with an evolving topography, processes which are relevant to the evolution of rift basins globally.

Sedimentary evolution and controlling factors of Early-Mid Miocene Deltaic systems in the Northern Pearl River Mouth Basin, South China Sea

The Pearl River Mouth Basin is located at the northern continental shelf of the South China Sea. Since the early Miocene, the Paleo-pearl river transported a large amount of sediments to the northwest of the basin and resulted in the formation of a large-scale river-delta depositional system, which has become an important oil and gas reservoir in the study area. In the current paper, we investigate the characteristics and evolution of fluvial-deltaic depositional systems and their controlling factors, including sea level change, tectonic subsidence and sediment supply on the basis of 3D seismic, well logging and core data. Early-Mid Miocene succession can be divided into two second-order sequences (CS1–CS2) and eight third-order sequences (S1–S8). Deltaic systems developed in S1–S2 are relatively coarse in grain size, and the delta plain deposits are dominated by thickly stacked (100–180 m) distributary channel sand bodies and interpreted as braided delta depositional system. In the early stage (S1–S2), the braided delta systems mainly distributed in the west of the Baiyun Sag, which were proceeded by a retreat to the south of the Enping Sag along with sharply rising sea level. Following the transgression of S2, the provenance of the Paleo-Pearl River extended to the coastal region of South China, and the papleoclimate changed from warm and humid to dry and cold in the early Miocene, leading to the development of transition of braided river delta to meandering river delta, which was characterized by relatively fine grain deposits. During the deposition of S3–S6, well sorted and rounded fine sandstones of deltaic front deposits accumulated in the study area. The retrogradation to accretion and subsequent progradation of these meander delta systems are attributed to the sea level change in the study area. During the deposition of S7–S8, the delta front retreated to the south of the Enping depression as a result of minor sea level rise, reduction in sediment input, and subsidence rate. This resulted in the development of a wave-controlled deltaic depositional system.

Depositional architecture, evolution and controlling factors of the Miocene submarine canyon system in the Pearl River Mouth Basin, northern South China Sea

Submarine canyon system in the Miocene Pearl River Mouth Basin, northern continental margin of the South China Sea, records the process of sediments transported from shelf margin to advanced abyssal plain and comprises important petroleum reservoirs in the basin. Based on integrated analysis of seismic, well logs and core data, the sequence framework, depositional architecture and controlling factors of the submarine canyon system are well documented. As a composite sequence bounded by regional unconformity, the Zhujiang Formation (CS1) can be divided into 5 sequences (CS1-1-CS1-5), and the lower CS1-2 and CS1-3 are the main strata that the submarine canyon system developed. The submarine canyon system can be divided into five segments (A-E) by their distinct geomorphology and depositional architectures. From Segment A to E, the channels in the submarine canyon system transform from “V” shaped single channel, “U” shaped single channel, “gull-wing” shaped channel-levee complex, “W” shaped branch channels to mound shaped distal composite channel and front splay deposits. This is accordantly consistent with sedimentary process of the channels transitional from erosional, erosional-aggradational, aggradational and then lateral migrational. The changing interaction of multi-source sediment supply, differential tectonic subsidence and relative sea level change are considered to be the major control on the development and evolution of the submarine canyon system. The differential tectonic subsidence since the Late Oligocene produced the adequate slope angle, sufficient accommodation and distinct basin geomorphology for the development and segmentation of the submarine canyon system. Slope-gully to slope fan deposits fed by the shelf margin delta systems from the Paleo-Pearl River and the northeastern Dongsha Uplift converged into the submarine canyon system, providing abundant sediments for its development. Relative sea level changes, especially the two regional regressions with abundant sediment supply have made great influence on the evolution of the submarine canyon system.

Spatial and temporal variability of sediment infilling and episodic rifting in the North Pearl River Mouth Basin, South China Sea

Pearl River Mouth Basin (PRMB) is a typical episodically rifting basin, and its sediment records exhibit a multistage infilling process. To build the coupling relationship between the spatial variability of tectonic movement and sediment dispersal pattern, we character the source-to-sink system distribution within continental margin and analysis their dominated factors with quantitative statistical methods. First, we identify the faults and calculate the rifting rate by interpreting the two-dimensional (2D) seismic data and zircon or apatite fission-track data (ZFT/AFT). Accordingly, based on the various trending of the rifting rate evolution, we classified rifting process episodically into three patterns: accelerated rifting decelerated rifting, and uniform rifting. Then, we integrated the data available on detrital zircon U–Pb, rare earth element, and heavy mineral assemblage to identify the responding S2S components associated with the above various rifting processes. Results show that in the first tectonic stage during the early Eocene, the sediments were mainly sourced from an intrabasin provenance area, whereas in the late Eocene to the Oligocene, the paleo-Pearl River provided the sediments to the sink area. We restore the facies association of the sink area by studying the core samples, electric well logs, and three-dimensional (3D) seismic data. During the accelerated and uniform rifting processes, coarse-grained deposited along the boundary faults, which includes the fan delta and subaqueous fans. During decelerated rifting, the depositional environment was dominated by braided channels, meandering channels, and tide-influenced channel accretion. Based on the quantitative analysis the relationship between the grain size of the sediment in each S2S segment and the rifting rate, more fine-grained components were preserved in the decelerated rifting system, while coarse-grained sediments fill the accelerated rifting depression and uniform rifting components. Furthermore, the sediment supply and relative height can influence the volume of the S2S system in the uniform rifting system. In the decelerated rifting basin, the sediment supply is the major factor associated with the development of S2S, whereas the relative height is the major factor associated with the accelerated rifting basin.

Using element geochemistry and detrital zircon geochronology to constrain provenance of the Eocene sediments in the deep-water area of the Pearl River Mouth Basin, South China Sea

• The Eocene parent rocks formed in an island arc-active continental margin setting. • These sediments were mainly derived constantly from local topographic highs. • The Panyu Low Uplift began to receive sediments of South China since the late Eocene. As the largest sag in the Zhu II Depression within the Pearl River Mouth Basin, the Baiyun Sag (BYS) lies in an area of interaction among the Eurasian Plate, Pacific Plate, and Indian Plate. The BYS mainly experienced the Paleogene rift stage and Neogene–Quaternary post-rift stage. Thick syn -rift sediments in the BYS have recorded the nature of provenance and provide an excellent record of regional tectonic evolution prior to the opening of the South China Sea. In this study, elemental geochemical analysis combined with published zircon detrital U-Pb dating results are applied to better understand the provenance change and tectonic setting of the BYS during the Eocene. In this respect, the chondrite normalized REE patterns of Eocene samples from six wells are highly similar to upper continental crust (UCC) and post-Archean Australian shale (PAAS), particularly with respect to LREE enrichment, significantly negative Eu anomalies, and slight Ce anomalies. Geochemical results confirm that the BYS Eocene sediments were derived from a continental island arc to an active continental margin. In addition, the rock types of sources and the relatively narrow detrital zircon ages show that Mesozoic intermediate-felsic igneous and metamorphic rocks derived from local topographic highs contributed to infilling most of the BYS. Furthermore, the results show that the Panyu Low Uplift began to accept large sediments transported by the paleo-Pearl River from the South China coast during the active syn -rift stage, prior to the opening of the South China Sea.

The formation and evolution of the paleo-Pearl River and its influence on the source of the northern South China sea

The paleo-Pearl River has been suggested as one of the major source terrains for the northern South China Sea, which headstreams in the hinterland of the Tibetan Plateau and flows through the South China Block, eventually discharges into the Pearl River Mouth Basin (PRMB) of the South China Sea (SCS). However, the drainage history of the paleo-Pearl River remains a matter of debate. Detrital zircon UPb ages, trace elements, Nd and Sr isotopes and clay minerals from the Eocene to Miocene sediments in the Pearl River Mouth Basin of the South China Sea have been used to investigate the sedimentary provenance and reconstruct the drainage history of the paleo-Pearl River. The Eu/Eu*, La/Sc, La/Co, Th/Sc and Th/Co ratios, the HfLa/Th and La/Sc-Co/Th diagrams, and the chondrite normalized REE patterns of the samples suggested that the Eocene to Miocene sediments were mainly derived from felsic source rock. The Lower Eocene sediments were mainly provided by the intrabasinal uplift regions. The Dong River and Bei River initiated since Upper Eocene supplied large amounts of felsic detritus from the Southern China Coast to Zhu Ⅰ Depression, and then transported sediments into the Zhu Ⅱ depression during the upper Early Oligocene. The Nd and Sr isotopes of the sediments suggested that the Liu River may not provide sediments for the PRMB, however, the Gui River may have made a very small contribution. The Nd and Sr isotopes of the sediments also suggested that the paleo-Pearl River began to extend westward to form Xi River and eventually the Hongshui River in the Late Oligocene. The trace element ratios of the samples also suggested that the Miocene sediments may have received more input from an intermediate rock area, indicating the main provenance switch from the coast of South China to a northern source during this time. This conclusion has been supported by the detrital zircon UPb ages, Nd and Sr isotopes and clay minerals data of the samples, which show that the provenance of the sediments supplied by the paleo-Pearl River had an abrupt shift in the Middle Miocene. The southeastern Tibetan Plateau rapid uplifted and experienced erosion in the Middle Miocene, leading to the progressive headward erosion of the Pearl River system into the continental interior.

Detrital zircon geochronology reveals source-to-sink relationships in the Pearl River Mouth Basin, China

A major challenge in provenance and source-to-sink analysis is deciphering intrabasinal versus extrabasinal sediment sources and processes. This issue is well-illustrated by the Paleogene Pearl River Mouth Basin (PRMB), whose provenance reflects a combination of sediments eroded from the Cathaysia Block (CB), southeastern China, and from intrabasinal structural highs. Here we use new detrital zircon UPb ages from Paleogene formations in seven boreholes, southern PRMB, to investigate such local versus regional influences on provenance. Detrital zircons from the upper Eocene-lower Oligocene Enping Formation are dominated by Jurassic-Cretaceous ages, with a 125–110 Ma age-cluster, absent in modern river data from the CB and diagnostic of intrabasinal sediment sources. In the northern part of the basin, Mesozoic-dominated zircon age-spectra give way to Paleozoic and Precambrian grains, a pattern also recognized for the late Oligocene Zhuhai Formation, suggesting a major change in provenance likely related to extrabasinal influence from the CB. The age spectra for these samples are most similar to the northeastern Pearl River, narrowing this region as the most likely source. Spatial analysis of the results suggests that during deposition of the Enping Formation, sediment transport was not uniform and that the basin's architecture strongly influenced provenance, with structural highs acting as both sediment sources and barrier to sediment transport from the CB; whereas structural lows, with clear extrabasinal influence, functioned as sediment transport corridors. Such spatial differences are lost in samples from the Zhuhai Formation and their provenance suggests that the paleo-Pearl River and tectono-climatically driven surface processes in the CB dominated deposition thereafter.

Using seismic geomorphology and detrital zircon geochronology to constrain provenance evolution and its response of Paleogene Enping Formation in the Baiyun Sag, Pearl River Mouth Basin, South China sea: Implications for paleo-Pearl River drainage evolution

The syn-rift sedimentary history of the Pearl River Mouth Basin (PRMB) in the northern South China Sea is poorly understood due to restricted borehole coverage. In this study, an integrated analysis of 3D seismic data, detrital zircon data and the data from previous provenance studies has been used to document the shifting of provenance and depositional response during the Paleogene Enping Formation of the Baiyun Sag in the PRMB. Our results show that the Baiyun Sag was filled mainly with sediments derived from two potential sources: the intrabasinal source of uplifts in the PRMB (Mesozoic igneous rocks) and the extrabasinal source of the South China Block (Precambrian–Paleozoic metamorphic and magmatic rocks). During the deposition of the lower and middle members of the Enping Formation (EpL–EpM), the sediment of the Baiyun Sag was derived primarily from the intrabasinal source. The sediment was transported over relatively short distance through faulted troughs and incised valleys and deposited in a series of small-to medium-scale braided deltas, beach bars and fan deltas. However, during the deposition of the upper member of the Enping Formation (EpU), the sediment of the Baiyun Sag was derived mainly from a mixture of extrabasinal and intrabasinal sources. The sediment of the EpU was transported over relatively long distance via large-scale incised valleys and deposited in three stages large-scale progradational braided delta. The detrital zircon age spectra of the EpU in the northwestern area show four well-recognized age clusters with peaks at ∼842 Ma, ∼450 Ma, ∼252 Ma and ∼151 Ma, which correspond to tectono-magmatism in the South China Block. The analysis of provenance shifting in this study may be of great value in constraining the tectonic and sedimentary evolution of the PRMB, northern South China Sea margin, as well as the drainage evolution of the paleo-Pearl River. Our findings can also provide potential benefits for the integrated analysis of geophysics and geochronology data through time in the petroliferous basins.

The effect of river-delta system on the formation of the source rocks in the Baiyun Sag, Pearl River Mouth Basin

Source rock formation influenced by river-delta system, especially in continental margin basins, is still poorly understood. This article aimed to reveal the effect of river-delta system on the formation of the source rock by taking the Baiyun Sag of the Pearl River Mouth Basin for example. Paleo-Pearl River began to develop since the Enping Formation, providing abundant organic matter beneficial for the formation of the source rocks in the Baiyun Sag. The main controlling factor of source rock formation in the Baiyun Sag is terrestrial organic matter supply rather than the paleoproductivity or redox conditions. Low Al/Ti and P/Ti ratios suggest low marine productivity, which may be associated with a large number of terrigenous detritus input, occupying about 43.04%–94.91%. There is a positive correlation between the oleanane/C30hopane ratio and the TOC value, showing that terrigenous organic matter controls the source rock formation. The size of the delta below Pearl River estuary determines the extent of terrestrial organic matter supply. Source rocks with high organic matter abundance mainly formed in delta environment, and those in neritic environment in Enping and Zhuhai Formations also have high TOC values as a result of adequate terrestrial organic matter supply.

Provenance of heavy mineral deposits on the northwestern shelf of the South China Sea, evidence from single-mineral chemistry

Abstract A study of heavy mineral geochemistry has been carried out in order to examine the potential sources of heavy mineral deposits within surficial sediment on the northwestern shelf of the South China Sea. Tourmaline, amphibole and garnet from six samples near the coast and eleven samples on the shelf were analyzed by an electron microprobe. Chemical varieties of tourmaline and amphibole indicate that the Pearl River is the main supplier of sandy sediments on the eastern shelf within a 100 km radius west of the paleo-deltas. Sandy sediments on the western shelf are mainly sourced from the Jian River and the Wanquan River. Heavy mineral placers on the middle and outer shelves are mainly derived from reworking of the paleo Pearl River deltas. Heavy mineral placers in the west are mainly sourced from the small rivers and are distributed in the sandy deposits near the coasts. This study demonstrates that the occurrence of heavy mineral placers on wide continental shelf is mainly determined by the sediment supply and marine processes during transgressions.

Influences of Tibetan Plateau uplift on provenance evolution of the paleo-Pearl River

A comparative analysis of the geochemical characteristics of sediments from the Oligocene Zhuhai Formation (32–23.8 Ma), the Miocene Zhujiang Formation (23.8–16.5 Ma), and the Hanjiang Formation (16.5–10.5 Ma) and a comprehensive analysis of the geochemical characteristics of rocks surrounding the paleo-Pearl River drainage contribute to understanding the influences of the Tibetan Plateau uplift on provenance evolution of the paleo-Pearl River. The results show that the geochemical characteristics of sediments from the Oligocene Zhuhai Formation are very different from the geochemical characteristics of sediments from the Miocene Zhujiang and Hanjiang Formations. The ∑ rare earth elements (REE) of mudstone is relatively high in the Zhuhai Formation, 204.07–293.88 ppm (average 240.46 ppm), and low in the Zhujiang and Hanjiang Formations, 181.32–236.73 ppm (average 203.83 ppm) and 166.84–236.65 ppm (average 199.04 ppm), respectively. The chemical index of alteration (CIA) for these samples has a similar trend to the ∑ REE: the CIA of the Zhuhai Formation is relatively high and the CIA of the Zhujiang and Hanjiang Formations is relatively low. The uplift of the Tibetan Plateau is crucial to the westward expansion of the paleo-Pearl River drainage.

Holocene delta evolution and sequence stratigraphy of the Pearl River Delta in South China

We analyzed the sedimentary characteristics and chronostratigraphy of the Pearl River Delta in South China, and discussed the Holocene stratigraphic characteristics and the filling process since the Holocene, based on 90 boreholes. Our results showed that the maximum transgressive surface of the Pearl River Delta was located in the soft marine silt horizons, whereas it was shown as an erosion surface in areas with tidal scour. From bottom to top, Holocene sedimentary sequences were fluvial facies, floodplain-estuary facies, and estuary-delta facies in the paleo-valley, while the paleo-interfluve sequences were described as littoral facies, estuary facies, and delta facies. Vertical accumulation sequences of Holocene sediments were shown primarily as positive tapering-shaped sequences with no typical foreset, topset, or other sedimentary sequences of the Gilbert Delta. The paleo-Pearl River estuary had different evolution models in the highstand systems tract (HST) compared with other large deltas worldwide, in that it is dominated by a unique and complex geomorphologic boundary, and that it is a multi-sourced delta compounded by the independent and parallel development of fluvial sedimentary bodies with different scales. A huge estuary was formed in the present Pearl River Delta area when the post-glacial transgression reached maximum at about 6 ka BP. The estuary was divided into two parts by obstruction of a series of islands, an upper part composed of the semi-enclosed inner paleo-bay connected to rivers and a lower part consisting of the outer paleo-bay connected to the ocean. Both of these areas were interlinked by only a few narrows, in which the fluvial sediments are accumulated primarily in the inner paleo-bay. During 6-2 ka BP, the sedimentation in various regions of the inner paleo-bay occurred simultaneously with independent development under the remodeling and transformation effect of complex boundaries on river and ocean dynamics. After 2 ka BP, the evolution of the delta is no longer a simple natural process, but rather a common remodeling process accomplished by nature and humans.

Sedimentary development of the Pearl River Estuary based on seismic stratigraphy

The Pearl River Estuary in the Southern China was studied both by applying concepts of seismic stratigraphy to the interpretation of high resolution seismic profiles and by correlating with borehole records. The correlation between seismic facies and borehole stratigraphy of the estuary enables to propose a seismic stratigraphy model of the estuarine infill. The stratigraphy and evolution of the Holocene succession of the estuary were reconstructed. The history of estuarine sedimentary development consists of five stages represented by 5 seismic units bounded by laterally sub-continuous seismic interfaces and being consistent with the 5 borehole subdivisions: (i) The basal stage deposits, represented by BU and the borehole section P, might represent the paleo Pearl River alluvial deposits in the Late Quaternary. (ii) The stage I deposits, represented by SU1 and the borehole section A, might be late glacial prodeltaic deposits that occurred during Marine Isotope Stage 3 highstand. (iii) The stage II deposits, represented by SU2 and the borehole section B, consist of relatively coarse-grained sediments deposited during the post glacial transgression about 20–10 ka BP. (iv) The stage III deposits (SU3 and the borehole section C) were generated when the rate of sea level rise decreased in ∼ 20–10 kz BP, which forced sediments to be deposited inside the estuary, where a tidal ravinement surface was characterized by strong erosions and channel formations in the outer zone of the estuary. (v) The stage IV deposits (SU4 and the borehole section D) are the infillings of the estuarine highstand progradation during the last 6000 yrs when the sea surface almost reached the present level.

Marine sand resources in the Pearl River estuary waters of China

Marine sand is one of the most important marine mineral resources in the Pearl River estuary as well as nearby Hong Kong waters of China. For more healthy and order development of marine sand extraction activities, about 518 km of initial seismic exploration and marine drilling of 5 validation boreholes with total footage of 176.7 m were carried out in 2001 and 2002 respectively, and the preliminary overall situation of marine sand resources in the Pearl River estuary waters was clarified. Based on geological interpretation of GeoPulse seismic profiles and core sample analyses of boreholes, the Quaternary stratigraphic sequence in the Pearl River estuary was divided into four depositional units: the upper marine unit of Holocene marine mud, and other three late Pleistocene units: the upper terrestrial unit of weathered mottled clay, the lower marine unit of silty clay, and the lower terrestrial unit of alluvial sand. The main type of marine sand occurrence and the main exploration targets for marine sand resources are identified in the late Pleistocene paleo-Pearl River channel sand at the lower terrestrial unit. The most valuable marine sand resources are located in Holocene tidal channel which coincide with late Pleistocene paleo-channels where the Holocene marine mud overburden is thinner. Sustainable development and scientific management of marine sand resources in the Pearl River estuary waters must strengthen legal system construction, work out scientific exploitation planning, strengthen environmental impact research, and strictly enforce pertinent laws. In about 3000 km 2 Pearl River estuary waters tentative estimation of reserves of buried marine sand is 12.5 × 10 8 m 3 in 20 sites, of which 10 sites with 5.38 × 10 8 m 3 were suggested to be suitable for current exploitation, other part of these reserves were put aside for exploitation as their thick cover in 4 sites with 2.75 × 10 8 m 3, seriously contaminated cover in 1 site with 2.5 × 10 8 m 3 or ecological or environmental sensitivity in 5 sites with 5.38 × 10 8 m 3. This research results can give some overall description of marine sand resources in the Pearl River estuary waters and provide scientific base for macroscopic management. Gassy sediments recorded by acoustic turbidity change the geoacoustic properties of the seabed, weaken geophysical exploration effect, and have great engineering and environment significance.

Baiyun movement: A significant tectonic event on Oligocene/Miocene boundary in the northern South China Sea and its regional implications

A significant geologic event occurred on the Oligocene/Miocene boundary at 23.8 Ma in the northern South China Sea, which is named the Baiyun (白云) movement in this article. This event strongly affected not only the South China Sea, but also East Asia. After the Baiyun event, the ridge of seafloor spreading of the South China Sea jumped southward and rotated counterclockwise, and a strong subsidence occurred in the Baiyun sag of the Pearl River Mouth basin. The shelf break shifted suddenly from the south to the north of the Baiyun sag, and the deposition environment in this sag changed from continental shelf with neritic deposition to continental slope with deep-water deposition. Sediment geochemistry study indicated that the Baiyun event played a key role in the rapid change of sediment provenance for the Pearl River Mouth basin. Between 32 and 23.8 Ma, the source of sediments was mainly from the granites in South China, while after 23.8 Ma some sediments might have come from the eastern Himalaya, as the Pearl River drainage extended westward after the uplift of Tibet since that time. The Baiyun event led to a great change in the drainage framework of the paleo-Pearl River, sediment types and the depositional environments in the Pearl River Mouth basin, and relative sea level of the northern South China Sea, as well as sedimentation and hydrocarbon accumulation in the area.

Denudation history of South China block and sediment supply to northern margin of the South China Sea

On the basis of apatite fission track (AFT) analyses, this article aims to provide a quantitative overview of Cenozoic morphotectonic evolution and sediment supply to the northern margin of the South China Sea (SCS). Seventeen granite samples were collected from the coast to the inland of the South China block. Plots of AFT age against sample location with respect to the coastline show a general trend of youngling age away from the coast, which implies more prolonged erosion and sediment contribution at the inland of the South China Sea during post break-up evolution. Two-stage fast erosion process, Early Tertiary and Middle Miocene, is deduced from simulated cooling histories. The first fast cooling and denudation during Early Tertiary are recorded by the samples along the coast (between 70 and 60 Ma) and the inland (between 50 and 30 Ma), respectively. This suggests initial local erosion and deposition in the northern margin of the SCS during Early Tertiary. Fast erosion along the coast ceased since ca. 50 Ma, while it had lasted until ca. 30 Ma inland, indicating that the erosion was transferred from the local coastal zone initially toward the continental interior with unified subsidence of the northern margin, which resulted in the formation of a south-dipping topography of the continental margin. The thermal stasis in the South China block since ca. 30 Ma must define the time at which the northern margin became dynamically disconnected from the active rifting and stretching that was taking place to the south. The lower erosion rate is inconsistent with higher sedimentary rate in the Pearl River Mouth basin during Late Oligocene (ca. 25 Ma). This indicates that the increased sedimentation in the basin is not due to the erosion of the granite belt of the South China block, but perhaps points to the westward propagation of the paleo-Pearl River drainage related to the uplift of the eastern margin of Tibet plateau and southward jumping of spreading axis of the South China Sea. The second erosion acceleration rate of the Middle Miocene (ca. 14 Ma) cooling could have been linked to the long-distance effect of uplift of the Tibet plateau or due to the enhanced East Asian monsoon.

Sequence Stratigraphy of Deep-water Fan System of Pearl River, South China Sea

The Baiyun Sag located in the deep-water continental slope region and on the down dip side of the paleo-Pearl River and of the large sand-rich Pearl River delta in shallow continental shelf is a favorable area for developing large-scale deep-water fan system. The study of sequence stratigraphy of the deep-water slope area was guided by regional geological research, which led to the discovery of the deep-water fan system of Pearl River with multi-sequence overlapped. This discovery makes the Baiyun Sag a new prospective area for petroleum exploration. Besides admitting the resolution of different data, multiplicity of solutions and limitation in the interpretation of sequence stratigraphy, the study also emphasized the following aspects: the comprehensive application and mutual authentication of data from different disciplines; the control of periodic sea-level change on deposition; the validity of the identification of the isochronic horizon of seismic reflection phases; the interactive identification of sequence boundary; the response of the sequence boundary to biostratigraphy, relative sea-level change and global eustacy; the response correlation between different sedimentary bodies in a sequence framework. The establishment of the sequence-stratigraphic framework leads to the discovery of the deep-water fan system of Pearl River. It reveals the coupling relationship among the Pearl River drainage area, the large-scale Pearl River delta on shelf and the Pearl River deep-water fan system on slope; the response relationship between the deep-water fan system of Pearl River and the sea-level change; the correlation between deep-water fans and paleogeography. The discovery of the deep-water fan system of Pearl River greatly promotes petroleum exploration in the deep-water slope area of the South China Sea.

Deep‐water Fan Systems and Petroleum Resources on the Northern Slope of the South China Sea

Abstract The shallow shelf delta/strand arenaceous‐pelitic deposit region in the north of the Pearl River mouth basin, sitting on the northern continental shelf of the South China Sea, has already become an important oil production base in China. Recent researched has revealed that a great deal of deep‐water fans of great petroleum potentiality exist on the Baiyun deep‐water slope below the big paleo Pearl River and its large delta. Based on a mass of exploration wells and 2‐D seismic data of the shallow shelf region, a interpretation of sequence stratigraphy confirmed the existence of deep‐water fans. The cyclic falling of sea level, abundant detrital matter from the paleo Pearl River and the persistent geothermal subsidence in the Baiyun sag are the three prerequisites for the formation and development of deep‐water fans. There are many in common between the deep‐water shelf depositional system of the northern South China Sea and the exploration hotspots region on the two banks of the Atlantic. For example, both are located on passive continent margins, and persistent secular thermal subsidence and large paleo rivers have supplied abundant material sources and organic matter. More recently, the discovery of the big gas pool on the northern slope of the Baiyun sag confirms that the Lower Tertiary lacustrine facies in the Baiyun sag has a great potentiality of source rocks. The fans overlying the Lower Tertiary source rocks should become the main exploration areas for oil and gas resources.